# MatCreateSubMatricesMPI
Extracts MPI submatrices across a sub communicator of mat (by pairs of `IS` that may live on subcomms). 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatCreateSubMatricesMPI(Mat mat, PetscInt n, const IS irow[], const IS icol[], MatReuse scall, Mat *submat[])
```
Collective


## Input Parameters

- ***mat -*** the matrix
- ***n   -*** the number of submatrixes to be extracted
- ***irow, icol -*** index sets of rows and columns to extract
- ***scall -*** either `MAT_INITIAL_MATRIX` or `MAT_REUSE_MATRIX`



## Output Parameter

- ***submat -*** the array of submatrices





## Note
This is used by `PCGASM`


## See Also
 `Mat`, `PCGASM`, `MatCreateSubMatrices()`, `MatCreateSubMatrix()`, `MatGetRow()`, `MatGetDiagonal()`, `MatReuse`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/interface/matrix.c.html#MatCreateSubMatricesMPI">src/mat/interface/matrix.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/adj/mpi/mpiadj.c.html#MatCreateSubMatricesMPI_MPIAdj">MatCreateSubMatricesMPI_MPIAdj in src/mat/impls/adj/mpi/mpiadj.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/mpi/mpiov.c.html#MatCreateSubMatricesMPI_MPIXAIJ(Mat C, PetscInt ismax, const IS isrow[], const IS iscol[], MatReuse scall, Mat *submat[], PetscErrorCode (*getsubmats_seq)(Mat, PetscInt, const IS[], const IS[], MatReuse, Mat **), PetscErrorCode (*getlocalmats)(Mat, Mat *, Mat *), PetscErrorCode (*setseqmat)(Mat, IS, IS, MatStructure, Mat), PetscErrorCode (*setseqmats)">MatCreateSubMatricesMPI_MPIXAIJ(Mat C, PetscInt ismax, const IS isrow[], const IS iscol[], MatReuse scall, Mat *submat[], PetscErrorCode (*getsubmats_seq)(Mat, PetscInt, const IS[], const IS[], MatReuse, Mat **), PetscErrorCode (*getlocalmats)(Mat, Mat *, Mat *), PetscErrorCode (*setseqmat)(Mat, IS, IS, MatStructure, Mat), PetscErrorCode (*setseqmats) in src/mat/impls/aij/mpi/mpiov.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/mpi/mpiov.c.html#MatCreateSubMatricesMPI_MPIAIJ">MatCreateSubMatricesMPI_MPIAIJ in src/mat/impls/aij/mpi/mpiov.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/mat/interface/matrix.c)


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